1. Technical Field
The present invention relates to an optical measurement device, or the like, for measuring an optical rotation angle.
2. Related Art
It is possible to know the composition of a material without making direct contact by measuring light which has passed through the material. For example, it is possible to estimate concentration of a material by measuring an angle of optical rotation. Optical rotation refers to a property in which, when linearly polarized light passes through an optically active substance such as glucose, for example, a plane of polarization thereof rotates.
As a technology using the property of optical rotation, a technology is disclosed in WO 99/30132, for example, in which linearly polarized light which has passed through a test object is orthogonally separated, polarized components thereof are received by two respective light receiving elements, and an angle of optical rotation is measured from a difference between output levels of both the light receiving elements.
In the technology of measuring an angle of optical rotation which is disclosed in WO 99/30132, the angle of optical rotation is measured from a difference between output levels of the two light receiving elements. However, there is a problem in this measuring method. As light which is radiated to the test object, laser light is generally used, however, there is a case in which an output fluctuation, which is referred to as a so-called return light noise, occurs in a laser device such as a semiconductor laser which outputs laser light. It is a phenomenon in which oscillation of a laser becomes unstable since a part of light which is output from the laser device returns to the laser device again by being reflected. In this case, a so-called fluctuation in amount of light occurs in which amount of light of transmitted light which has passed through the test object fluctuates.
In addition, when a test object having a plurality of components whose absorbance is different from each other is measured, each component is not necessarily distributed equally in the test object. That is, the fluctuation in amount of light of transmitted light which passes through the test object easily occurs, since the absorbance becomes different depending on a mixed state of each component, a radiated position of the laser, the passage of time, or the like when performing the measuring.
When such a fluctuation in amount of light occurs, it is not possible to guarantee that the angle of optical rotation, which is simply calculated from a difference between received light levels in the light receiving elements, is a correct measurement value. This is because, when the fluctuation in amount of light occurs, the received light levels in the light receiving elements are totally changed, and the difference between the received light levels is changed. For example, though it is an extreme example, when amount of light of the transmitted light is reduced to ½, a difference between received light levels is reduced to ½, since the light receiving level in the light receiving element is reduced to ½. Consequently, the method of measuring an angle of optical rotation in the related art determined from the difference in received light levels, is unable to provide the correct angle of optical rotation.